Linkedin is at least as powerful at driving traffic per click as a Twitter Tweet or a Facebook Like, according to Clearspring, a provider of those sharing buttons you often see at the top and bottom of web pages.

Clearspring makes AddThis, a tool that allows brands and publishers to select and install buttons for Facebook Likes, Twitter Tweets and Linkedin Shares on their web sites.

Sharing buttons are becoming increasingly important to advertisers. A recommendation from a friend or colleague in a social network can be much more influential on your propensity to visit a web site than an ad on the TV or radio. Nissan's "Damned Ponies" ad, for instance, got 14 million views on YouTube in 2011 making it one of the most shared ads of the year.

They're crucial for ad sales, too: No traffic equals no ad exposures.

Linkedin doesn't drive as much total traffic as Facebook or Twitter because its network of members is much smaller than either of those companies. But on a per-share basis, it's at least as effective, according to Greg Cypes, director of product at Clearspring in McLean, Va.

For every article a user "shares" with her network, LinkedIn drives an average of 1.5 clicks back to the publisher. "That is better than the average across all of our networks, of about 1.1 clicks, and is about as effective as Twitter," Cypes says.

The networks available from AddThis include the obvious -- Facebook, Twitter -- along with the not-so-obvious, such as Messenger, Orkut and Vkontakte, a Russian social network. The network also includes the "print" and "email" buttons, which you've probably used without realizing they were sharing tools.

Over the following pages we' 'll examine the power of Linkedin Share, its place in the social media universe, and what it all means for advertisers and publishers.